The present invention relates to an inner lens type lens barrel assembly and an assembling method therefor.
In video cameras, for example, there has been used an inner-focus type lens barrel assembly which attains focusing by moving element lenses of a compensator lens group, a master lens group and the like along the optical axis in small steps. An example of that is shown in FIGS. 13 and 14 (see JP 3089500 B).
In this lens barrel assembly 1, a first movable lens frame 3 which holds a variator lens 2 for use of zooming and a second movable lens frame 5 which holds a master lens 4 for use of focusing are driven directly by rotation of driving shafts 8, 9 performed by an upper-and-lower pair of stepping motors 6, 7. In this case, the driving shafts 8, 9 have four functional roles as motor shafts, drive transmission shafts, sliding shafts and anti-rotation shafts.
The first movable lens frame 3 that holds the variator lens 2 and the second movable lens frame 5 that holds the master lens 4 are basically identical in structure to each other except that they are up-down inverse to each other. FIG. 14 shows structures of the first, second movable lens frames 3, 5. The structure of the first movable lens frame 3 is explained below with reference to FIG. 14.
The first movable lens frame 3 has an upper portion 3a and a lower portion 3c. The upper portion 3a extends along the direction of an optical axis C of the variator lens 2, and bearing portions are provided thereon at one end and the other end in the optical axis direction so as to be erected in directions perpendicular to the optical axis C. Then, V-grooves 3b, 3b are provided at upper sides of the bearing portions, and the driving shaft 8 is supported from the lower side and guided by these two V-grooves 3b, 3b. On an outer wall of one of the two bearing portions that is positioned outer in the optical axis direction, one board portion of an elastic member 10 which is formed of an L-shape bent board is fitted and fixed, where a clearance hole 10a which allows the driving shaft 8 to be inserted therethrough is provided at the one board portion. On the other hand, the other board portion of the elastic member 10 has elasticity, and a rack portion 10b is provided at its end portion so as to engage with a lead screw portion 8a of the driving shaft 8 from the upper side.
At a lower portion 3c of the first movable lens frame 3, a generally U-shaped guide groove 3d having an opening on its lower side is provided so as to extend vertically. By the lower side driving shaft 9 being inserted into the guide groove 3d, the first movable lens frame 3 is prevented from rotating about the upper side driving shaft 8.
In this way, the first movable lens frame 3 is prevented from rotation by the lower side driving shaft 9 being inserted into the guide groove 3d of the lower portion 3c, while the V-grooves 3b, 3b of the bearing portions in the upper portion 3a support the upper side driving shaft 8 from the lower side and moreover the rack portion 10b engages with the lead screw portion 8a of the driving shaft 8 from the upper side by the elastic force of the elastic member 10. Accordingly, as the driving shaft 8 is driven into rotation by the stepping motor 6, the variator lens 2 is enabled to reciprocate along the optical axis C together with the first movable lens frame 3.
Meanwhile, the second movable lens frame 5, as described above, has a structure up-down inverse to the first movable lens frame 3. Therefore, the second movable lens frame 5 is prevented from rotation by the upper-side driving shaft 8 being inserted into a guide groove 5d of an upper portion 5c, while V-grooves 5b, 5b of bearing portions in a lower portion 5a support the lower side driving shaft 9 from the upper side and moreover a rack portion 11b is engaged with a lead screw portion 9a of the driving shaft 9 from the lower side by the elastic force of an elastic member 11. Accordingly, as the driving shaft 9 is driven into rotation by the stepping motor 7, the master lens 4 is enabled to reciprocate along the optical axis C together with the second movable lens frame 5.
In addition, reference numerals 12, 13 denote lens barrel assemblies, 14 denotes a focus lens, 15 denotes an optical low-pass filter, and 16 denotes a CCD (Charge Coupled Device) unit.
However, the prior art lens barrel assembly disclosed in JP 3089500 B has problems shown below.
That is, the driving shafts 8, 9, which have four functional roles as motor shafts, drive transmission shafts, sliding shafts and anti-rotation shafts, are supported by different parts that are the front-side lens barrel assembly 12 and the rear-side lens barrel assembly 13, respectively. Due to this, the driving shafts 8, 9 may easily tilt, so that they are likely to be entangled and immobilized when the first movable lens frame 3 and the second movable lens frame 5 move along the optical axis C, problematically. Then, if the front-side lens barrel assembly 12 and the rear-side lens barrel assembly 13 are provided as a part having an integrated structure for solution of the above problem, it would become impossible to insert and assemble the first, second movable lens frames 3, 5 to the driving shafts 8, 9 in the direction of the optical axis C, posing a problem of degraded assemblability.
Also, the driving shafts 8, 9 are provided in a lead screw structure. Due to this, in the case where the driving shaft 8, 9 is inserted and assembled to the first, second movable lens frame 3, 5 in the direction of the optical axis C, there is a fear that inserting the driving shaft 8, 9 into the first, second movable lens frame 3, 5 might cause the rack portions 10b, 11b to be damaged because the rack portions 10b, 11b of the L-shaped elastic members 10, 11 fixed to the first, second movable lens frames 3, 5 are arranged to be engaged with the lead screw portions 8a, 9a by elastic force.
Therefore, in the case where the rack portion 10b, 11b is inserted while being bent toward a direction of separating from the driving shaft 8, 9 against the elastic force of the elastic member 10, 11 in order to prevent the rack portion 10b, 11b from being damaged, it may occur in some cases that the other board portion of the L-shaped elastic member 10, 11 is plastically deformed erroneously beyond its limitation of elastic deformation. In such a case, the elastic force of the other board portion would decrease, so that the rack portion 10b, 11b would no longer be engaged with the lead screw portion 8a, 9a, problematically.